1. Field of the Invention
The present invention relates to a layered structure suitable for use with sensor arrays a piezoelectric body, such as infrared sensors, ultrasonic sensors, and pressure sensors, actuator arrays, patterned memories, and the like. The invention also relates to a piezoelectric device using the layered structure.
2. Description of the Related Art
For I/O devices, small and light weight wearable devices are desired for portable use and ambient devices that fit in the environment are desired for stationary use in order to achieve the goal of realizing a ubiquitous society. From the viewpoint of ease of use and safety, it is important that these devices are “light weighted, not easily broken, and flexible”. Consequently, a trend towards flexibilization in various devices has recently been accelerated.
Whereas the flexibilization in the field of displays and electronic papers in wearable and ambient device configurations is moving forward steadily, the flexibilization of devices that use a piezoelectric material, such as various types of sensors, actuators, memories, and the like, is making little progress due to the fact that high temperature film forming of 600° C. or more is generally required for the manufacture of an inorganic piezoelectric material having excellent piezoelectricity and thereby a high heatproof temperature is required for the flexible substrates.
For piezoelectric materials that do not require high temperature film forming, piezoelectric polymers in which the piezoelectric substance itself has piezoelectricity as typified by polyVinylidene difluoride (PVDF) are known as described, for example, in U.S. Patent Application Publication No. 20100068460. The piezoelectric polymers, however, have a small piezoelectric d constant in comparison with inorganic piezoelectric materials, and therefore, they are limited to certain applications, such as pressure sensors and the like, that do not require a high piezoelectric performance.
Further, an attempt has been made in which a piezoelectric device is formed on a device forming substrate using a piezoelectric material which has high piezoelectricity, then the device forming substrate is removed by etching, and the piezoelectric device is bonded to a flexible substrate as described, for example, in claim 11 of Japanese Unexamined Patent Publication No. 2003-179282.
As described in Japanese Unexamined Patent Publication No. 2003-179282, it is necessary to use an adhesive when a thin film piezoelectric material is bonded to a flexible substrate. As a thin film piezoelectric material having a lower electrode layer formed on the bonding surface with a flexible substrate is actually used, the bonding using an adhesive may possibly result in that the adhesive hinders favorable contact between the piezoelectric film and electrode. Where the flexible substrate is a resin substrate, the piezoelectric film can not follow the deformation of the substrate due to differences in the rigidity and modulus of elasticity, whereby the piezoelectric film may have a crack or the piezoelectric film may be peeled off due to detachment of the adhesive.
The present invention has been developed in view of the circumstances described above, and it is an object of the present invention to provide a layered structure which includes a piezoelectric film that shows an excellent piezoelectric performance and can be applied favorably to flexible piezoelectric devices. It is a further object of the present invention to provide a flexible piezoelectric device using the layered structure.